web-vitals/src/types/ttfb.ts

Easily measure performance metrics in JavaScript

/*
 * Copyright 2022 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import type {Metric} from './base.js';

/**
 * A TTFB-specific version of the Metric object.
 */
export interface TTFBMetric extends Metric {
  name: 'TTFB';
  entries: PerformanceNavigationTiming[];
}

/**
 * An object containing potentially-helpful debugging information that
 * can be sent along with the TTFB value for the current page visit in order
 * to help identify issues happening to real-users in the field.
 *
 * NOTE: these values are primarily useful for page loads not handled via
 * service worker, as browsers differ in what they report when service worker
 * is involved, see: https://github.com/w3c/navigation-timing/issues/199
 */
export interface TTFBAttribution {
  /**
   * The total time from when the user initiates loading the page to when the
   * page starts to handle the request. Large values here are typically due
   * to HTTP redirects, though other browser processing contributes to this
   * duration as well (so even without redirect it's generally not zero).
   */
  waitingDuration: number;
  /**
   * The total time spent checking the HTTP cache for a match. For navigations
   * handled via service worker, this duration usually includes service worker
   * start-up time as well as time processing `fetch` event listeners, with
   * some exceptions, see: https://github.com/w3c/navigation-timing/issues/199
   */
  cacheDuration: number;
  /**
   * The total time to resolve the DNS for the requested domain.
   */
  dnsDuration: number;
  /**
   * The total time to create the connection to the requested domain.
   */
  connectionDuration: number;
  /**
   * The total time from when the request was sent until the first byte of the
   * response was received. This includes network time as well as server
   * processing time.
   */
  requestDuration: number;
  /**
   * The `navigation` entry of the current page, which is useful for diagnosing
   * general page load issues. This can be used to access `serverTiming` for
   * example: navigationEntry?.serverTiming
   */
  navigationEntry?: PerformanceNavigationTiming;
}

/**
 * A TTFB-specific version of the Metric object with attribution.
 */
export interface TTFBMetricWithAttribution extends TTFBMetric {
  attribution: TTFBAttribution;
}